The invention relates to medical and environmental diagnostics employing soybean peroxidase in place of horseradish peroxidase which has been historically used.
Enzymes are now widely used in medical and environmental diagnostics. Horseradish peroxidase has been one of the most satisfactory enzymes but is relatively expensive. It has now been found that soybean peroxidase can be readily harvested from soybean hulls at minimal expense and be substituted for horseradish peroxidase in these diagnostic chemistries.
Several diagnostic chemistries using the enzymatic activity of horseradish peroxidase have been described in the literature. Horseradish peroxidase has been used for diagnostic determinations of various analytes and has been used as a label in enzyme labeled antibodies used in the determination of immunologically reactive species (i.e. immunoassays) Such determinations can be carried out in solution or in dry analytical elements.
One type of useful assay utilizes enzymatic reactions wherein the analyte, upon contact with the appropriate reagents, reacts with oxygen in the presence of a suitable enzyme to produce hydrogen peroxide in proportion to the concentration of the analyte. A detectable product such as a visible or fluorescent dye is then produced by the reaction of hydrogen peroxide in proportion to the concentration of the analyte in the tested liquid Peroxidase is generally used in such assays to catalyze the oxidation of the interactive composition by hydrogen peroxide One example of such an assay is a glucose assay using glucose oxidase Glucose is oxidized in the presence of oxygen by the enzyme, glucose oxidase, to produce glucolactone and hydrogen peroxide. In the presence of peroxidase, the hydrogen peroxide oxidizes a colorless dye such as tetramethylbenzidine to produce a colored product.
Another type of assay utilizes an immunologically reactive compound such as an antibody. These chemistries can be generally classified into two groups, namely, conjugate or enzyme labeled antibody procedures, and non-conjugate or unlabeled antibody procedures. In the conjugate procedures, the enzyme is covalently linked to the antibody and applied to a sample containing the immobilized antigen to be detected. Thereafter the enzyme substrate, e.g., hydrogen peroxide, and an oxidazable chromogen such as a leuco dye are applied. In the presence of the peroxidase, the peroxide reacts with the chromogen resulting in the production of color. The production of color indicates the presence and in some cases the amount of the antigen. In another method, a competing substance is used to dislodge an antibody enzyme conjugate from an immobilized substrate, leading to an absence of color.
In a method sometimes referred to as the sandwich assay or enzyme linked immunoadsorbent assay (ELISA), a first antibody is bound to a solid support surface and challenged with a fluid sample suspected to contain the antigen to be detected and an enzyme-antibody conjugate. The antigen complexes with the antibody and the conjugate bonds to the antigen. Subsequent introduction of the substrate and chromogen produces a visual indication of the presence of the antigen.
Procedures employing non-conjugated enzymes include the enzyme bridge method and the peroxidase-antiperoxidase method. These methods use an antiperoxidase antibody produced by injecting peroxidase into an animal such as a goat, rabbit or guinea pig. The method does not require chemical conjugation of the antibody to the enzyme but consists of binding the enzyme to the antigen through the antigen-antibody reaction of an immunoglobulin-enzyme bridge. In the enzyme bridge method a secondary antibody acts as an immunologic bridge between the primary antibody against the suspected antigen and the antiperoxidase antibody. The antiperoxidase antibody in turn binds the peroxidase which catalyzes the indicator reaction. In the peroxidase-antiperoxidase method, a complex of the peroxidase and the antiperoxidase antibody is formed. This complex can then be used in the immunologic bridge method.